Evaluation of deep trap compensation ratio and recombination parameters by transient grating techniques

Abstract

We demonstrate a novel application of time-resolved transient grating technique for determination of deep trap occupation ratio in semi-insulating crystals. Light diffraction kinetics on a transient reflection grating with very small period (150 nm) provided conditions for studies of absorption nonlinearity and its discrimination from the coexisting free carrier and electro-optic ones. By numerical modeling of absorption grating kinetics in subnanosecond time domain, we determined the contributions of the recharged deep traps and two-photon absorption to diffraction kinetics and evaluated in this way the deep trap compensation ratio in differently grown GaAs crystals. Moreover, the decay time of the absorption grating provided the rate of carrier capture to these dominant deep traps, which have been recharged under illumination. Using this feature, we were able to monitor the thermal annealing process in vanadium-doped CdTe crystals: it has not effected the charge state of vanadium related deep traps, but reduced the concentration of the active residual carrier capture centers in the crystal.